Thio-THIP, also known as 4,5,6,7-tetrahydroisothiazolo[5,4-c]pyridin-3-ol, is a low-potency GABAA receptor very weak partial agonist or antagonist related to gaboxadol (THIP). It is also a weak GABAA-ρ receptor antagonist and a weak GABA reuptake inhibitor. The drug has three orders of magnitude lower potency as a GABAA receptor modulator than gaboxadol. This is unlike the case of muscimol and thiomuscimol, which are almost equipotent. Like gaboxadol, thio-THIP is a zwitterion. It may cross the blood–brain barrier similarly to gaboxadol. Thio-THIP was developed and described by Povl Krogsgaard-Larsen and colleagues by 1981.